Sheet metal rolling process



J. B. TYTUS 1,842,220

SHEET METAL ROLLING PROCESS Jan. 19, "1932.

Filed Jan. 8,. 1929 Mam; [11m WZZMY w D D 0 0v 0 0. ii \mi t i& Q 3 -mRQ g 623 5 QMQ x WZQQQQ L01 E Patented Jan. 19, 1932 UNITED STATESPATENT OFFICE JOHN B. TYTUS, OF MIDDLETOWN, OHIO, ASSIGINOR TO THEAMERICAN ROLLING MILL COMPANY, OF MIDDLETOWN, OHIO, A CORPORATION OFOHIO SHEET iami. ROLLING rnoorzss Application filed January 8, 1929.Serial No. 330,989.

My invention is of importance in sheet metal rolling processes in whicha hot rolling is followed by a cold rolling, and it is of.

particular importance in connection with the so called continuousmethods of rolling sheet metal. It will be described and may beunderstood to have a special application to processes involving therolling of sheets from wide strip; but my application is not restrictedthereto and it is equally as adaptable to the other processes in whichhot and cold working join in the production of a finished article. i

In such sheet rolling processes and particularly in continuous widestrip mills, there hasbeen a tendency toward the production of thinnergauges on the hot mill as a starting point for a. further cold rollingreduction. This tendency has greatly increased the importance of aserious problem in connection with these processes. This problem isconcerned primarily with non-uniformityin the product of the hot mills;and this non-uniformity may be due to a number of concurring causes.

In the first place, 1t is not possible to carry on the hot rolling stepat a uniformity of temperature in the piece and as between pieces. Thisresults in inequalities of strain in various parts of a sheet or stripand in inequalities of strain as between separate sheets and strips.There is no way of avoiding this, short of conducting the entire hotrolling operation with the metal heated at or above the critical rangeand this is impractical. Secondly, concurrent with these variations inresident strain in the product of the hot mill, there will be variationsin gauge. It is not practicable in rapid reduction processes in the hotmill rolling of single thickness pieces to comparatively thin gauges, todeliver a uniform product. There are no rolls available which will longwithstand the excessive wear resulting from rapid reduction processes.The result is that the piece develops roughness, the rolls cut out inthe active portions and do not give a piece which accurate as to gauge.In my copending application. Serial No. 227,600, I have described aprocess for obtaining, in a procedure involving rapid hot rolling reduction to thin gauge, a. product suitable for pack forming. This processinvolves a certain cold rolling step with attention to the transversecontour of the sheet, following the preliminary hot rollin and comingbefore hot rolling in packs. fily present invention has to do with theproduction of a product for a cold rolling step which product is in sucha condition that it may be reduced to the required gauge by cold rollingand will be substantially uniform.

WVe have as a product of the hot mill a sheet or strip which varies notonly in gauge but also in strain. As is well known, the existence ofthese irregularities is responsible for a number of defects in afinished sheet sufficient to justify rejections in a deep drawmgproduct. My present invention is concerned with the ultimate eliminationof these defects; but it is primarily concerned with the production ofan ultimate product which shall be uniform in gauge.

It is a fact in cold rolling that a product which shows both variationsin gauge and 1n strain as it comes from the hot mill will also showproportionate variations in these particulars at the exit end of thecold rolls. The exact reasons why this is so may not be entirely clear;but if the resident strain inequality in the material is removed, thecold rolls will, in a substantial reduction, bring about substantialuniformity of gauge,- that is to say, that whereas gauge variationspersist practically proportionately in a cold rolled product where thestrains accompanying initial gauge variations are present, they do notpersist in proportion at all where the initial product was not badlystrained nor strained with great irregularity, or where the strains havebeen removed.

An object of my invention therefore is to provide as the startingproduct of a cold rolling operation, a sheet or strip which, Whilecharacterized possibi'y by gauge inequalities, is characterized bysubstantial. absence of strain and substantial equality of such residentstrains as have not been removed.

It is a further object of my invention to produce this preliminaryproduct less expensively than has been possible hitherto.

It is still another object of my invention to secure in such a startingproduct a comparatively thin gauge, and in the production thereof torelieve the hot mills of extra duty.

It is still a further object of my invention to cut down the cost of theannealing and pickling steps which may intervene between the hot rollingand cold rolling 0perations.

These and other objects of my invention which will be pointed outhereinafter or will be apparent to one skilled in the art upon readingthese specifications, I accomplish by that certain process of which Ishall now describe a preferred embodiment having to do with theproduction of sheets from wide strip, it being understood that myprocess is equally applicable to the production of other rolled articlesfrom sheets or other starting forms which are not comprised within theterm wide strip. Reference is hereby made to'.

the drawing which accompanies this specification in which is illustrateddiagrammatically the steps of my process as set forth in the exemplaryembodiment which I shall now describe.

As hitherto pointed out, when, in the prodnot of the hot mill,irregularities of gauge and strain exist, gauge irregularities willpersist through the cold rolling step. It is possible to anneal betweenthe hot rolling and the cold rolling, but this is expensive. It involvescareful time and temperature control because the strains in the hotrolled product are comparatively slight and as is well known, a muchmore careful controlled annealing treatment is required to equalize andwipe out comparatively slight strains than is required for comparativelygreat strains. Annealing also involves a pickling step before subsequentcold rolling. Further it is to be pointed out here that all of thedifiiculties so far discussed are increased many fold in the practise ofhot rolling to comparatively thin gauges for the purpose of securing aproduct which may be cold rolled to gauge without intermediateannealings. Each intermediate annealing involves further expense anddifiiculty together with further pickling, which is highly undesirable.

My invention broadly comprises hot rolling to a comparatively lightgauge followed by red rolling, annealing, pickling and then coldrolling.

The most obvious initial advantage of this process is that it relievesthe hot mill of duty by the amount of actual reduction produced in thered rolling.

Secondly, the red rolling increases the residual strain in the metal tosuch an extent that a very much less carefully controlled andconsequently a less expensive annealing process will serve to eliminatethe strains. I

Thirdly, there is no annealing or pickling step between the hot rollingand the red rolling, which again saves expense. Thus my process is notanalogous to a process involving hot rolling, pickling, cold rolling,intervening annealing, pickling, and further cold rolling.

Thus I secure from the hot mill a product which in general commercialoperation will be unequal in gauge and will have resident straininequalities. By the amount of reduction in the red rolling operation, Irelieve the hot mill of duty. \Vithout any intervening annealing orpickling, I red roll the product of the hot mill. This red rolling is acold rolling carried on while the product is covered with the hot milloxide, which is the explanation for the name of the step. The residentstrain and gauge inequalities in the cold strip from the hot mill willnot be eliminated by the red rolling but will persist in substantialproportion in the product of that step. The reasons why this is so havebeen discussed above. But I have added to the resident hot mill strains,those produced by the red rolling operation; and I now have a productwhich has been considerably strained and which is suitable for quickannealing. Therefore it is susceptible to and is most advantageouslytreated by a continuous annealing in a tunnel furnace. the annealingbeing preferably carried on between the Al and A3 points. These aretermed critical points as defined at pages 530 and following of TheMaking. Shaping and Treating of Steel, Carnegie Steel Co.. secondedition. The time duration of the annealing treatment need not be longand the product can be comparatively quickly cooled thereafter withoutdetriment.

As the product of the red rolling step, I now have a sheet or strippossessing, commercially, inequalities of gauge but having the strainssubstantially removed therefrom. By the combination of the hot rollingand red rolling it will have been brought to a comparatively thin gaugewhich is suitable for cold rolling to gauge by a continuous operationnot involving intermediate annealings. Further. it is in such acondition that this cold rolling operation will reduce it to substantialuniformity of gauge.

With reference now to the drawing illustrating the production of sheetfrom wide stri by my process, I may start with a slab 1, which is heatedto hot rolling temperature in a slab furnace generally of the pushertype indicated at 2. Preferably I next roll the slab into a strip plateby a succession of passes through a universal mill 3. The still heatedstrip plate may then be rolled into a wide strip of considerable lengthin hot mills which are preferably tandem mills of fourhigh construction.'I have indicated at 4, 40, etc. a tandem of four four-high hot mills,at the end of which the strip designated as 14 may be coiled in a coil 5on a coiler 6. These coils will be cooled and held pending the next stepin the process. T heyare characterized, as explained, by inequalities ofgauge and of strain which cannot be avoided in commercial practice. Inthe next step the coil 5 is straightened in an uncoiler 7, and is passedone or more times through a red rolling mill 8, 8a. etc. which I haveshown as consisting of four stands of four-high cold rolls but which'mayin practice consist of one roll, or any expedient number. The productfrom the hot mill may, as an example but without limitation, be twelvegauge material and in the red rolling operation, it may be reduced tosixteen gauge; and-it may then be coiled into a coil 5a on a coiler 9 ofstandard construction.

The red-rolled coils 5a are next uncoiled and straightened by theuncoile'r 10 and are preferably fastened together for continuous'irocessing by any of the well known methods. I have indicated at 11 atraveling spot welder for the purpose. The continuous band of metal thusformed is next passed through a continuous annealing furnace 12 equippedwith a cooling duct 13. In this furnace the metal is heated topreferably between the A1 and A3 points and held for a length of timedepending upon the gauge and strain and is thereupon cooled with sometime lag by passage through the cooling duct. The combination of theresident strains of hot and cold work will produce in the coils 5a acondition suitable'for annealing without too long soaking. and withoutthe necessity for very slow cooling, so that the continuous apparatusindicated ,diagrammatically in the drawing will be found adequate forthe purpose. Continuous annealing furnaces are well known and require nodescription by me.

From the annealing furnace, the band of metal which I have indicated at14a is passed through a continuous pickling tank 15 which may beequipped with scrubbers and drying furnace 16 to a shear 17 which willshear it apart again into individual strips which are usuallycoiled-upon the coiler 18 into coils 5?) ready for the cold rollingoperation.

The cold rolling operation may be carried on in a tandem or fourfour-high cold rolls 19, 19a, etc. to which the metal is led'after thecoil 5?) is uncoilecl by the mechanism 20. At the end of the coldrolling operation, the metal may be recoiled by the mechanismQl into thecoils 50. It will be found that the metal has been reduced tosubstantial uniformity of gauge; and a further description of subsequentsteps in the production of finished sheets is not necessary by me.Various subsequent finishing processes may be used as for example, theprocess which is described in my copending application Serial No.333,263, filed Jan. 18, 1929 and which comprises, after such asubstantial cold rolling to gauge as is carried on in the cold rolls 19,etc., a continuous normalizing followed by pickling, shearing, boxannealing and skin passing or the like. Such processes have theadvantage among others of eliminating coiler break difiiculties and opensurface difficulties. As pointed out, the intermediate product asprepared for cold rolling in my present process is characterized bypractical absence of strains, but by the presence of gauge inequalitieswhich are afterwards eliminated by the cold rolling. The high portionsof the product however, receive more cold work than the lower ones andthus become harder, and ordinary annealing processes are commerciallyunsatisfactory for bringing the sheet to a condition of uniformityt= Theprocess described in my copending application referred to will do this.

It will be understood that my process, while it has been described withreference to'the instrumentalities and practices of making wide strip ofconsiderable length, is equally applicable to other sheet processes.Thus sheet bars may be broken down and then reduced to heavy gauge inthe hot mills either by hand or continuously. The heavy-gauge hot millsheets may then be cooled and redrolled cold. After this they will beannealed and pickled, which may be done by stitching the sheets togetheror otherwise fastening them, and proceeding continuously. Then they willbe sheared apart and cold rolled, being subsequently finished asdesired.

Skin passing as referred to in my specifications means finishing passesthrough the cold rolls. It is a term commonly used in the rolling art toindicate a finishing cold rolling whether merely for surfacing or for aslight hardening after annealing. It should be distinguished from coldrolling to gauge.

My process is directed to a solution of spe-- cialized problems, namely:those problems which have to do with the continuous rolling of sheetmetal. This is comparatively a new art. The problems manifestedthemselves in the fact that when it was desired to cold roll strip metalof sheet width to uniform gauge, the roller did not find himself able todo this in commercial practice. The reason was found to reside in thefact that the hot mills or whatever combination of process stepspreceded the cold rolling to gauge, delivered a piece of'metal for suchcold rolling which was characterized by considerable gauge and straininequality; and while a cold rolling to gauge, if it effected a veryconsiderable reduction, could bring metal to uniform gauge, it couldonly do to strain and gauge; but this is not possible in continuousrolling, because continuous rolling methods imply an absence ofcontinuous skillful attention to the rolls to adjust them to theparticular conditions surrounding the rolling of each piece. The gaugeand strain inequality trouble is characteristic of continuous rollingmethods.

Persons have tried to anneal continuousl the hot mill strip sheet orsheets as the case may be, but this has not been altogether sue--cessful, partly because the strains in the hot mill product, whileunequal, are not large enough in the aggregate to permit of a quickcontinuous annealing. Other remedies for the situation have beenproposed with which my present invention is not concerned. My remedy asset forth herein, is to cold roll the hdt mill strip or other pieces,with the hot mill oxide still on them, thereby (.1) etfecting a furtherreduction and relieving the hot mills of duty to some extent, and (2) soincreasing the inherent strain in the metal pieces that they can beremoved by a quick annealing. It is well known that the more heavily themetal is strained, the quicker will be the erasing of these strains in aheat treatment.

Various modifications can of course, be nade in my invention withoutdeparting from that specific series of steps which will be set forth inthe appended claims. The apparatus may be modified as desired.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent, is

1. That process of producing sheet metal which comprises hot rolling apiece to materially reduce its thickness. cold rolling said piecewithout removal of the hot mill oxide therefrom, afterward heat treatingand pickling said piece to prepare it for cold rolling and cold rollingit to gauge with substantial reduction and without interveningannealings.

2. That process of producing sheet metal which comprises effecting apreliminary reduction of metal in a hot mill, cold rolling the reducedpiece without removal of the hot mill oxide therefrom to an extentsuflicient to produce a further reduction and increase the strainstherein, relieving said strains by a brief heat treatment, and furtherreducing the thickness of said ,piece to uniform gauge by cold rolling,

3. That process of producing sheet metal which comprises rolling metalto sheet width and a thickness greater than desired for cold rolling togauge. cooling said metal. red rolling said metal to the desired gaugefor cold rolling, annealing said metal and cot-d rolling itto gauge.

4:. That process of producing sheet metal which comprises hot rollingwith a substanneeaaao rolling said metal without removal of the hot milloxide, annealing and thereafter cold rolling it to gauge withoutintervening annealings.

7. That process of producing sheet metal which comprises hot rollingsaid metal, and without removal of the hot mill oxide, cold rolling saidmetal to increase the strains therein, to such an extent that they maybe removed by quick continuous annealing, annealing and pickling saidmetal and cold rolling it to gauge with a substantial reduction andwithout intervening annealings.

8. That process of producing sheet metal which comprises hot rollingsaid metal to heavy gauge thereby producing a product characterized bygauge and strain inequalities, cold rolling said metal thereby producinga product also characterized by gauge and strain inequalities but inwhich the strains have been increased to such an extent that they may besubstantially removed by briefly heating said metal to between its A1and A3 points followed by a quick cooling thereof, removing said strainsubstantially from said metal by a quick heating thereof, to between theA1 and A3 points followed by a quick cooling, whereby a product isproduced characterized by gauge inequalities but substantial absence ofstrains, and cold rolling said product to gauge with a substantialreduction and without intervening anneallngs.

9. That process of producing sheet metal which comprises interposingbetween the hot rolling and cold rolling steps in each of which asubstantial reduction is effected, a red rolling whereby the gauge ofthe hot mill product is further reduced and the material straightsued bycold work, and annealing said metal between the red rolling and coldrolling steps. 1

10. That process of producing sheet metal 7 which comprises hot rollingand cold rolling said metal before any annealing, thereafter annealingsaid metal and cold rolling it to gauge with a substantial reduction andwith out intervening anncalings.

JOHN B. TYTUS.

